(1) Field of the Invention
The present disclosure generally relates to flow-directing elements such as vanes and blades used in gas turbine engines, and more specifically to flow-directing elements, airfoil inserts and assemblies of flow-directing elements and airfoil inserts and assemblies of flow-directing elements and airfoil inserts.
(2) Description of the Related Art
Gas turbine engines extract energy from expanding gases in a turbine section disposed immediately downstream of a combustor section. Alternating stages of flow-directing elements, for example stationary vanes and rotating blades, operate at elevated temperatures. The operational temperatures may, in some instances, exceed the melting temperature of their base material. For this reason, flow-directing elements in a turbine utilize thermal barrier coating systems and various cooling systems to improve their durability.
One type of cooling system is a convective cooling system. A convective cooling system utilizes coolant, such as pressurized air from a forward compressor section of the gas turbine engine, to remove heat from the flow-directing elements. The coolant circulates through internal cavities and passages, removing heat via convection, before exiting. Various features and separate details are known to increase the heat transfer coefficient of the coolant inside flow-directing elements. One such detail is a perforated airfoil insert, also known as an impingement tube or a baffle tube.
When disposed inside an internal cavity and spaced from the cavity wall, the insert improves heat removal. The coolant discharges from the perforations in high velocity jets, spraying across the gap between the insert and cavity wall. By impinging against the cavity wall, the heat transfer coefficient increases thus enhancing the cooling effectiveness.
Airfoil inserts are generally affixed to the flow-directing element to prevent liberation and possible engine damage. Since the flow-directing element typically has a greater coefficient of thermal expansion than the insert, only one end of the insert is affixed, while the other end is left free. Relative movement between the insert's free end and the flow-directing element opens a gap between the insert and the flow-directing element at the free end. The gap allows a portion of the high-pressure coolant exiting the insert to leak back between the insert and the cavity wall. This leaking coolant interferes with the impingement cooling jets, thus reducing the heat transfer coefficient and cooling effectiveness.
Those skilled in the art will recognize that it is preferable to minimize the volume of coolant leaking back into the cavity between the insert and flow-directing element. An enhanced seal between the free end of an insert and a flow-directing element is therefore needed.